节点JS：错误[ERR_HTTP_HEADERS_SENT]：发送到客户端后无法设置标头

Question

Beginner here. I understand that the below error message occurs when the api tries to set the response more than once. And i also realize the asynchronous characteristics of node js.

But still i am unable to debug the issue. Please help me out.

router.route("/new").post((req, res) => {

  //Variable declarations
  sql.open(connectionString, function(err, conn){
    var pm = conn.procedureMgr();
    pm.callproc('dbo.AddRequestDetails',[request_zone,request_type,requester_type,request_flow,
      sales_order,requester_email,quotation,request_reason,request_status,
      StatusFlag, bot_status,bot_comments,additional_notification_to,additional_information, approver,
      old_value,new_value,new_shipping_point,partner_name,text_type,text_type_action,table_data], function(err,results,output){
      console.log("Hi");
        if (err != null) {
        console.log("error",err.message);
        var user =  req.ge('User');
        var scriptName = path.basename(__filename);
        var value = {err: err.message, user: user, scriptName:scriptName};
        axios.post(configData.SERVER_URL + "/api/logToDB", value);
        res.status(400).json(err.message);
      } else {
        console.log("Data successfully added in Main Table & Sub Table");
        res.json("Data successfully added in Main Table & Sub Table");
      }
      
    });
  });
});

module.exports = router;

And my output appears like below.

Hi
Data successfully added in Main Table & Sub Table
POST /api/add/new 200 44.882 ms - 51
Hi
Data successfully added in Main Table & Sub Table
_http_outgoing.js:558
    throw new ERR_HTTP_HEADERS_SENT('set');
    ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they
are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:558:11)
    at ServerResponse.header (C:\Users\C572103\Documents\One
Order Change\OOC Portal\backend\node_modules\express\lib\response.js:767:10)
    at ServerResponse.send (C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\express\lib\response.js:267:15)
    at C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\routes\uploadData.js:58:13
    at Object.callback (C:\Users\C572103\Documents\One Order
Change\OOC Portal\backend\node_modules\msnodesqlv8\lib\procedure.js:233:13)
    at onProcedureRaw (C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\msnodesqlv8\lib\procedure.js:60:22)
    at C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\msnodesqlv8\lib\reader.js:199:15
    at onStatementComplete (C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\msnodesqlv8\lib\driver.js:185:11)
    at Object.end (C:\Users\C572103\Documents\One Order Change\OOC Portal\backend\node_modules\msnodesqlv8\lib\driver.js:318:19) {
  code: 'ERR_HTTP_HEADERS_SENT'
}

I am using msnodesqlv8 for sql operations

Answer 1

似乎您要在发送响应后设置响应的标头（如 res.setHeader(400)），控制 if else 语句，似乎它在发送 200 后输入错误 else

Answer 2

It's very obvious from your code that Hi is called twice. My guess is that you're opening a new sql connecting using sql.open , but you never close it. Even though you send the result to the response, the connection is still opened and some listeners might fire again, even though on another request.

Also check if in a single request pm.callproc does only one thing and then does not fire two callbacks, because basically that's the real issue - you try to send two responses for the same request.